Toner

Abstract

A toner comprises a toner particle and an external additive, the toner satisfies a certain relationship with regard to σl (C/m 2 ) and σs (C/m 2 ). The toner is divided into two groups i.e. a first group and a second group with inertial classifier, the first group including a larger size of the toner particles, and the second group including a smaller size of the toner particles, and the number of the toner particles in the first group being substantially equal to the number of the toner particles in the second group. Then, al (C/m 2 ) represents an absolute value of average surface charge density of the toner included in the first group, and σs (C/m 2 ) represents an absolute value of average surface charge density of the toner included in the second group.

What is claimed is: 
     
       1. A toner comprising a toner particle and an external additive,
 the toner satisfying a relationship expressed by the following formula (1);
   0.10≤σ l/σs≤ 0.75  (1),
 
 
 where 
 when the toner is divided into two groups, i.e. a first group and a second group with an inertial classifier, the first group including a larger size of the toner particles, and the second group including smaller size of the toner particles, and the number of the toner particles in the first group being substantially equal to the number of the toner particles in the second group, 
 σl (C/m 2 ) represents an absolute value of average surface charge density of the toner included in the first group, and 
 σs (C/m 2 ) represents an absolute value of average surface charge density of the toner included in the second group. 
 
     
     
       2. The toner according to  claim 1 , wherein a median diameter D50 of the toner in terms of particle number is 3.0 μm or more and 6.0 μm or less. 
     
     
       3. The toner according to  claim 1 , wherein a median diameter D50 of the toner in terms of particle number is 3.0 μm or more and 5.0 μm or less. 
     
     
       4. The toner according to  claim 1 , wherein an absolute value Qs of an average electric charge amount per toner particle included in the second group is 1.4 fC or more. 
     
     
       5. The toner according to  claim 1 , wherein an absolute value Ql of an average electric charge amount per toner particle included in the first group is 2.8 fC or less. 
     
     
       6. The toner according to  claim 1 , wherein the values of σl and σs satisfy a relationship expressed by the following formula (2);
   0.10≤σ l/σs≤ 0.67  (2).
 
 
     
     
       7. The toner according to  claim 1 , wherein the value of σs is 0.038 C/m 2  or more. 
     
     
       8. The toner according to  claim 1 , wherein the value of σl is 0.028 C/m 2  or less. 
     
     
       9. The toner according to  claim 1 , wherein an absolute value of an electric charge amount per unit mass Q/M of the toner is 70 μC/g or less, when, in an environment at 23° C. and at 50% RH, 0.7 g of the toner and 9.3 g of a standard carrier (N-01) according to Imaging Society of Japan are put in a polyethylene bottle having the capacity of 50 mL and are shaken at 200 rpm for five minutes with a shaker to be electrically charged by friction. 
     
     
       10. The toner according to  claim 1 , wherein a span value of the toner expressed by the following formula (3) is 0.7 or more and 2.0 or less;
   ( D 90− D 10)/ D 50  (3),
 
 where D90 is a particle size on cumulative 90% in terms of particle number, and D10 is a particle size on cumulative 10% in terms of particle number. 
 
     
     
       11. The toner according to  claim 1 , wherein
 the external additive includes an external additive having negative chargeability. 
 
     
     
       12. The toner according to  claim 11 , wherein the external additive in the second group has a higher degree of negative chargeability than the external additive in the first group. 
     
     
       13. The toner according to  claim 11 , wherein the toner included in the first group is coated with silica particles having a water absorption content of 1.0% or more, and the toner included in the second group is coated with silica particles having a water absorption content of 0.5% or less. 
     
     
       14. The toner according to  claim 11 , wherein values of Cs and Cl satisfy a relationship expressed by the following formula (4);
   0.10≤ Cl/Cs≤ 0.80  (4),
 
 where the Cl is a coating ratio of the toner included in the first group with the external additive having negative chargeability, and the Cs is a coating ratio of the toner included in the second group with the external additive having negative chargeability. 
 
     
     
       15. The toner according to  claim 14 , wherein the values of Cs and Cl satisfy a relationship expressed by the following formula (5);
   0.10≤ Cl/Cs≤ 0.67  (5).
 
 
     
     
       16. The toner according to  claim 1 , further comprising a charge control agent having chargeability, wherein
 values of CAs and CAl satisfy a relationship expressed by the following formula (6);
   0.10≤ CAl/CAs≤ 0.80  (6),
 
 
 where the CAl is a content of the charge control agent in the toner included in the first group, and the CAs is a content of the charge control agent in the toner included in the second group. 
 
     
     
       17. The toner according to  claim 16 , wherein the values of CAs and CAl satisfy a relationship expressed by the following formula (7);
   0.10≤ CAl/CAs≤ 0.50  (7).